Nickel-chromium alloys



United States Patent F The present invention relates to nickel-chromium alloys and, more particularly, to nickel-chromium alloys which are adapted to be employed as precision cast components l in structures subjected in use to the deleterious effects of high temperature, high stress and corrosive atmospheres. In nickel-chromium alloys employed for the aforementioned purpose which have been known heretofore, it is desirable to use as high a chromium content as possible, since it improves their resistance to oxidation. Nevertheless, the maximum chromium content has been limited to about since it has been found that at higher chromium contents the creep resistance of the alloys at high temperatures falls off. Although attempts werem'ade to provide a nickel-chromium precision casting alloy having good oxidation resistance in combination with an excellent overall combination of room temperature and elevated temperature characteristics, none, as far as I am aware, was entirely successful when carried into practice commercially on an industrial scale.

It has now been discovered that alloys containing more than 15% chromium can be provided which alloys have particularly good stress-rupture lives at high temperatures 3,093,476 Patented June 11, 1963 0.20% carbon, from about 0.005% to about 0.15% boron and from about 0.3% to about 0.7% zirconium. Advan tageously, the alloys can contain less than about 5% cobalt. In addition, the alloys can contain from 0% to about 0.5 silicon, from 0% to about 0.5% manganese and from 0% to about 0.5 iron. The balance of the alloys is essentially nickel and includes impurities and incidental elements in amounts which do not adversely vafiYect the novel and basic characteristics of the alloys.

The contents of titanium (Ti), chromium (Cr), and

'cobalt (Co), expressed as percentages by weight, must comply with the following relationship:

;f(TiCoCr) =0.8 TiCoCr+ 10.4 TiCo-+1.13 TiCr +1.75 CoCr 19.2 Co -1l Cr+ 8.4 Ti+ 123 0 When the titanium, cobalt and chromium contents of the alloys are plotted in three-dimensional coordinates, the equation f(TiCoCr)=0 defines, a surface which divides the volume defined by the compositional limits of 1.5% to 4.5% titanium, 15% to 22% chromium and 0% to 15 cobalt into two parts and the alloys according to the inventionlie within this volume on one side of the surface.

It is found in practice that the alloys defined in this way are characterized by a stress-rupture life as cast of more than 60 hours when tested under a stress of 7 long tons per square inch (t.s.i.) (i.e., 15,680 pounds per square inch) at a temperature of 980 C.

Some examples of alloys according to the invention are given in Table I below, which also showsthe value of f(TiCoCr) given above:

Table l Composition percent Life, hnat 7 Alloy t.s.i.

O Zr A1 Cr Q0 Ti W Si Mn Fe B f(TiCoCr) 961) C. 980 Q.

The results given in Table. 11 below show how the stress-rupture lives of alloys (outside the present invention) otherwise within thecomposition of the limits 5 set out hereinbefore are impaired when the value of f(TiCoCr) is less than 0.

Table II Composition percent Lite, hnat 7. Alloy 12.51.

o Zr Al or 00 Ti W St Mn Fe B f(TiCoCr) 960C: 980C.

3 0.1 0. 5 4 20 0 2 8 O 0 0 '0. 05 36 25 4 0. l 0. 5 4 20 10 4 8 0 j 0 0 0.05 39 47 21 novel nickel-chromium alloy for use in structures adapted j..

to be employed at elevated temperatures under severe stress. I

Another object of the invention is to provide a novel, precision casting, nickel-chromium alloy for use as components in structures subjected in use tothe deleterious effects of elevated temperature, high stress and corrosive atmospheres.

Other objects and advantages will become apparent from the following description.

Generally speaking, the present invention contemplates When nickel-chromium base alloys are employed in gas turbine engines, they are sometimes corroded by the products of combustion. A measure of the extentfof this corrosion is given by immersing the alloys for one'hour I in a mixture containing sodium sulfate and 25% f(TiCoCr) 0 V and also the relationship f (TiCoCr) 0, where f TiCoCr) =0.057 TiCoCr+l.325 TiCo +3.944 TiCr+0.228 CoCr-5.32 C0 15.762 Cr80.225 Tia-319.25

3 The values of this function are given in Table III for Alloys 1 and 2, together with the corresponding weight losses in the corrosion test specified above. It will be seen that both of the alloys satisfy both relationships:

It is also desirable that alloys used under severe conditions of stress at very high temperatures should be reasonably ductile at room temperature. Preferably their elongation in room temperature tensile tests exceeds 4% before rupture occurs.

It is found that provided the alloys according to the invention also satisfy the relationship felongc where f (TiC0Cr)=-0.0l81 TlCOCf-I-QO437 CICO +0.2753 TiC0+0.3125 Ticl 0.6406 CO-1.25 CI-7.625 TIA-28.75

Table IV Elongation, Alloy N o /clong(TiC0Or) percent at room temperature The alloys according to the present invention are primarily intended for use in the as-cast state. It has been found, however, that certain of the alloys of the present invention which contain about 15% to 22% chromium, about 5% to 15% cobalt, about 7% to 9% tungsten, about 3.5% to 4.5% aluminum, about 1.5% to 4.5% titanium, about 0.01% to 0.20% carbon, about .005% to 0.15% boron and about 0.3% to 0.6% zirconium can be hot worked and can be used in the wrought condition after a suitable heat treatment to precipitate a Ni (Ti, Al) phase. In particular, alloys containing from 8% to 15% cobalt and from 1.5 to 3% titanium have good creep properties at elevated temperatures in the wrought state.

A suitable heat treatment consists in heating the alloys for 1 /2 hours at 1200 C., air-cooling to room temperature, then heating for 16 hours at 1050" C. and finally again air-cooling. After hot working and heat treatment in this way, Alloy 2, which contains 10% cobalt and 2% titanium, was found to have a life to rupture of 172 hours under a stress of 7 tons per square inch at 960 C., whereas Alloy 1, which contains no cobalt and 4% titanium, had a life of only hours under the same conditions.

It is to be noted that the alloys of the present invention are highly advantageous when compared as to overall characteristics with alloys such as Alloy A which nominally contains 0.1% carbon, 0.05 boron, 0.05% zirconium, 12% chromium, 10% cobalt, 8% tungsten, 4% aluminum, 4% titanium, with the balance being essentially nickel. The following schedule contains a numerical indication of the merit of the alloys of the present invention as compared to Alloy A (wherein the value of 4 indicates excellent, 3 indicates good, 2 indicates acceptable, 1 indicates poor and 0 indicates very poor) for various desirable characteristics of the alloys similar in purpose to the alloys of the present invention:

Schedule Alloys 0! Characteristics the present Alloy A invention stress rupture strength at 980 C 2 4 Room temperature ductility 3 .5 Room temperature strength 4 4 Resistance to sulfur laden ntmospheres 4 2 Castability 4 2 Resistance to oxidation"... 4 2 Resistance to thermal-fatigu 4 2 Total 25 10 It is to be noted that the total merit indicia set forth in the foregoing schedule clearly illustrate the overall superiority of the alloys of the present invention.

The alloys of the present invention are particularly adapted to be employed as articles such as turbine blades which are subjected in use to a combination of high stress, high temperature and corrosive atmospheres.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

I claim:

1. An alloy having an advantageous combination of high temperature and room temperature characteristics specifically adapted to be employed at elevated temperatures in contact with sulfur-containing atmospheres under high stress which consists essentially of more than about 15% to about 22% chromium, up to about 15% cobalt, about 7% to about 9% tungsten, about 3.5% to about 4.5% aluminum, about 1.5% to about 4.5% titanium, about 0.01% to about 0.20% carbon, about 0.005% to about 0.15% boron, about 0.3% to about 0.7% zironium, up to about 0.5% silicon, up to about 0.5 manganese, up to about 0.5% iron, the balance of the alloy being essentially nickel, the respective contents of titanium (Ti), chromium (Cr) and cobalt (Co), expressed as percentages by weight, being so correlated that the relationship 0.8 TiCoCr+10.4 TiCo+1.l3 TiCr +1.75 CoCr-l9.2 Co- 11 Cr+8.4 Ti+ 123 is greater than zero and said respective contents of titanium, chromium and cobalt being so correlated that the relationship -0.05 7 TiCoCr+ 1.325 TiCo+3.944 TiCr ,+0.228 CoCr-5.32 Co15.762 Cr80.225 Ti+319.25

is less than zero.

2. An alloy having an advantageous combination of high temperature and room temperature characteristics specifically adapted to be employed at elevated temperatures under high stress which consists essentially of more than about 15% to about 22% chromium, up to about 15 cobalt, about 7% to about 9% tungsten, about 3.5 to about 4.5% aluminum, about 1.5% to about 4.5% titanium, about 0.01% to about 0.20% carbon, about 0.005% to about 0.15 boron, about 0.3% to about 0.7% zirconium, up to about 0.5 silicon, up to about 0.5 manganese, up to about 0.5 iron, the balance of the alloy being essentially nickel, the respective contents of titanium (Ti), chromium (Cr), and cobalt (Co), ex-

pressed as percentages by weight, being so correlated that the relationship O.8 TiCoCr,+ 10.4 TiCo+1.13 TiCr +1.75 COCr19.2 C0-11 Cr+8.4 Ti-l- 123 is greater than zero, said respective contents of titanium, chromium and cobalt being so correlated that the relationship -0.057 TiCoCr+1.325 TiCo+3.944 TiCr +0228 CoC-r-5.32 Col5.762 Cr80.225 Ti+319.25

is less than zero and said respective contents of titanium,

6 chromium and cobalt also being so correlated that the relationship -0.0181 TiCoCr-l-0.0437 C-rCo+0.2753 TiCo +0.3125 TiC1'0.6406 C01.25 Cr7.625 Ti+28.75

is greater than zero.

References Cited in the file of this patent UNITED STATES PATENTS 10 2,809,110 Darmara 061. 8, 1957 2,920,956 Nisbet et a1. Jan. 12, 1960 2,951,757 Brown Sept. 6, 1960 

-0.8 TICOCR+10.4 TICO+1.13 TICR +1.75 COCR-19.2 CO-11 CR+8.4 TI+123 -0.057 TICOCR+1.325 TICO+3.944 TICR +0.288 COCR-5.32 CO-15.762 CR-80.225 TI+319.25 